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Re: Input sought on datatyping tradeoff

From: Peter F. Patel-Schneider <pfps@research.bell-labs.com>
Date: Fri, 12 Jul 2002 15:20:17 -0400
To: bwm@hplb.hpl.hp.com
Cc: www-rdf-interest@w3.org
Message-Id: <20020712152017K.pfps@research.bell-labs.com>

More unsupported assumptions and ohter comments:

From: Brian McBride <bwm@hplb.hpl.hp.com>
Subject: Input sought on datatyping tradeoff
Date: Thu, 11 Jul 2002 19:46:49 +0100

[...]

> It is important in getting the semantics correct that we distinguish 
> between a datatype value, e.g. the integer 10 and a lexical representation 
> of the value, e.g. the string "10".
> 
> We are proposing two principal idioms for representing datatyped 
> information.  The first looks like this:
> 
>    <Jenny> <age>          _:a .
>    _:a     <xsdr:decimal> "10" .

What does the object of the second triple above have to do with the
two-character string '10'?  I don't see any reason that literals are
strings.  In fact, I believe that in RDF they are *not* strings.

[...]

> Test A:
> 
>    <Jenny> <ageInYears> "10" .
>    <John>  <ageInYears> "10" .
> 
> Should an RDF processor conclude that the value of the ageInYears 
> properties for Jenny and John are the same?

Why should this question even make sense?  It may be that there is no
notion of equality, or even identity, for literals.

Why should an RDF processor care about equality or identity of literals?
Even if the RDF model theory has a notion of equality or identity of
literals and RDF processor only needs to know about this notion if it makes
a difference to the operation of the processor.

[...]

> These test cases only relates to the situation where there are no range 
> constraints on the properties.

This deserves to be put in large, bold, red flashing type at the top of the
message.

> Now for a different kind of test.  How do the values of the two idioms relate?
> 
> Test D:
> 
>    <Jenny>      <ageInYears> "10" .
>    <ageInYears> rdfs:range xsd:decimal .
> 
>    <John>  <ageInYears>   _:a .
>    _:a     xsdr:decimal   "10" .
> 
> Should an RDF processor conclude that Jenny and John have the same 
> age?  

Again, should an RDF processor conclude that any two syntactic constructs
are ``the same''?  Does it make a difference to the operations of an RDF
processor.?

Further, what does ``the same'' mean?  Is it some semantic notion?  Is it
some syntactic notion?  Does it, perhaps, mean identical, as in ``denote
the same object in the model thoery'', or is there some weaker notion of
equality that should be used?

> It is not possible to have the answers to Tests A and Test D both be 
> yes.  Either the A's can be yes or D can be yes, but not both.  We have to 
> decide which of these is the most important to have.

This may depend on what ``the same'' means.

[...]

>    tidy) the <ageInYears> property takes a value which is a numeral, i.e. a 
> string

As I understand it, tidy RDF literals are not even strings, but instead are
structured data.  It is even the case that in XML/RDF under the tidy
literal reading, two occurences of the same character data can end up
denoting different data structures.

Peter F. Patel-Schneider
Bell Labs Research
Received on Friday, 12 July 2002 15:21:45 GMT

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